We’ve all been tickled. We all know our ticklish spots, and we all know how we respond when these are tickled: helpless laughter, attempts at escape, perhaps screaming and retaliation.

Is this a universal response among humans, or – like some other physical sensations and reactions – does it depend on culture? And for that matter, why do we react this way at all to this particular kind of touch?

In an attempt to find out, Netherlands-based researchers Ziliang Xiong and Konstantina Kilteni surveyed people from different cultures about their experiences of tickling and ticklishness. The results, published in Nature Human Behaviour, add to science’s slowly growing picture of this ordinary yet baffling phenomenon.

What the research found

The researchers recruited 149 people who spoke Chinese as their primary language, 150 who spoke Dutch, and 149 who spoke Greek, to fill in an extensive questionnaire about tickling.

Xiong and Kilteni focused on the strong laughter-inducing type of tickle called gargalesis. (This is different from the light, feather-like tickle sensation known as knismesis.)

The authors analysed these self-reports and found that there is no difference across the three cultures in the patterns of people who report being tickled and tickling others.

Nor did they find any differences between cultures in the places that are ticklish on the body.

To anyone who has thought about the phenomenon of ticklishness, the finding that there are no cultural differences in how people experience it is actually quite predictable. That’s not to say the research is not worth doing, as it’s always important to have data.

However, it does seem unlikely tickling would not be a deep-seated human behaviour, given that there is strong evidence that even other animals are ticklish.

Chimpanzees, gorillas, orangutans are all ticklish. Even rats show a similar response to a strong tickle – they make a sound very like a giggle.

An extremely common experience

According to the study, more than 98% of people have been tickled at least once, and more than 95% have tickled others. As you might expect, the most ticklish areas are the armpits, tummy and the soles of your feet.

When we’re tickled, we all tend to laugh, even if we don’t really like being tickled. We often resist and may try to escape, tickle back, or scream.

The social dynamics of tickling are also unsurprising. People are more likely to be tickled in childhood than adulthood. Ticklers are likely to be older than ticklees (and tickling others is more frequent in childhood than adulthood).

Xiong and Kilteni used the survey responses to make “body maps” of ticklish zones. The places on the body that are most ticklish were consistent across the three cultural groups surveyed.

5 theories of ticklishness

The authors used their maps of which body parts are most ticklish to test five major theories that seek to explain why we are more ticklish in certain places. The ticklishness of an area was not directly related to the density of receptors for touch, skin thickness, vulnerability due to proximity of major arteries, or how pleasurable touch to an area is.

Instead, the strongest relationship was between ticklishness and the frequency with which particular body areas are touched – with those less frequently touched being more ticklish. But actually, a theory that combines all of these factors had the best explanatory power, with touch exposure giving the most contribution.

Why ticklishness evolved

There are also various theories as to why being ticklish might have evolved, and has stuck around. It could be that being ticklish is protective because it allows us to be sensitive to detecting insects crawling on our skin, but this seems more relevant to the feather-light tickle of knismesis.

The intense experience of gargalesis, however, seems quite different. It is one of the first things that makes us laugh as infants, and has been proposed to be an important social activity – first, between caregivers and infants, later between other close family members and friends.

It has also been proposed that being ticklish trains us to protect our vulnerable parts, or acts like a reflex that moves us away from a potentially damaging stimulus.

We know the sensation of being tickled is primarily experienced when being tickled by another (or indeed by a machine), not when we try to do it ourselves.

This is because when we touch ourselves, we have two sources of information about what is going to happen – the motor program of the touching, and the actual experience of touch. Because the touch is expected and predictable, the brain adjusts our experience accordingly.

Overall, ticklishness has a lot of potential to help us understand how the brain processes different types of touch, social contexts, evolutionary pathways, and more. But we don’t yet know why we – and other animals – respond so strongly to this specific form of touch.